Tool rest for grinding wheel with automatic wear compensation

ABSTRACT

A movable tool rest for a grinder having a grinding wheel and a tool platform mounted adjacent the periphery of the grinding wheel wherein provision is made for adjusting automatically the position of the platform with respect to the periphery of the wheel as the wheel decreases in diameter due to wear.

United States Patent [1 1 Schaap et al.

[451 Jan. 1,1974

[54] TOOL REST FOR GRINDING WHEEL WITI-I AUTOMATIC WEAR COMPENSATION[75] Inventors: Sanford Schaap, Southfield; Borys Zura, SterlingHeights, both of Mich.

[73] Assignee: Ford Motor Company, Dearborn,

Mich.

[221 Filed: Feb. 2, 1972 [21] Appl. No.: 222,859

[52] US. Cl. 51/238 R, 5l/l65.87 [51] Int. Cl B24b 41/06 [58] Field ofSearch 51/l65.87, 165.88,

[56] References Cited I UNITED STATES PATENTS 980,164 [2/1910 Nichols5l/l65.88

Kundig 5l/l65.87 X

Hulse 5l/165.88

Primary ExaminerHarold D. Whitehead Assistant ExaminerNicholas P. GodiciAttorneyl(eith L. Zerschling et al.

[5 7] ABSTRACT A movable tool rest for a grinder having a grinding wheeland a tool platform mounted adjacent the periphery of the grinding wheelwherein provision is made for adjusting automatically the position ofthe platform with respect to the periphery of the wheel as the wheeldecreases in diameter due to wear.

6 Claims, 5 Drawing Figures PATENTED JAN T SHEEY 2 0f 3 PATENTEB JANI974 SHEEI 3 BF 3 TOOL REST FOR GRINDING WHEEL WITH AUTOMATIC WEARCOMPENSATION GENERAL DESCRIPTION OF THE INVENTION Most grinding wheelsfound in tool rooms comprise a high speed abrasive disc mounted forrotation about a horizontal axis and a platform supported on a fixedbase. Provision is made for adjusting manually the platform toward theperiphery of the grinding wheel. The adjustment mechanism usuallycomprises a slide that is anchored to a fixed base by clamping bolts.The plat form may be adjusted relative to the grinding wheel when thebolts are loosened to effect a predetermined clearance between theplatform and the periphery of the wheel. When the adjustment iscompleted, the bolts again are clamped thereby holding the platform in afixed position.

A tool or other object to be ground is supported on the platform andmoved manually into engagement with the periphery of the wheel. Thiseventually reduces the diameter of the wheel due to wear. The spacebetween the platform and the wheel changes as the diameter of the wheelis reduced. It is necessary periodically, therefore, to readjust theplatform by loosening the clamping bolts and sliding the platform towardthe wheel.

Our invention comprises an automatic mechanism for adjusting theplatform relative to the periphery of the wheel. It maintains apredetermined clearance between the edge of the platform and theperipheryof the wheel throughout the useful life of the grinding wheelregardless of changes in diameter due to wear. Itavoids the necessityfor manual adjustment of the platform and it prevents inadvertentcontact of the platform with the wheel during such adjustments.

By providing automatic adjustments of the platform with respect to thewheel, the grinding wheel becomes safer to operate. It becomes lesslikely, or even impossible, for the tool or workpiece to become wedgedbetween the periphery of the wheel and the edge of the platform. Whenthe platform is maintained in close proximity to the periphery of thewheel at all times regardless of changes in diameter of the wheel, moreprecision in grinding of the tool or workpiece also can be achievedwithout the necessity for periodic manual adjustments of the platform.Furthermore, since manual adjustment is not required, the total timerequired to accomplish a given grinding operation is reducedaccordingly.

A suitable dressing wheel can be mounted on the movable platformstructure. It may be advanced across the peripheral surface of the wheelat periodic intervals whenever dressing is required. The automaticadjustment feature that maintains the platform in registry with thewheel is effective also to position the dressing wheel.

The automatic adjustment feature comprises a contact wheel which engagesthe periphery of the wheel when the wheel is at rest. It is carried byone end of an actuating lever for the movable platform structure. Ashroud surrounds the contact wheel as well as the peripheral faces ofthe grinding wheel. As the grinding wheel rotates, the viscous sheerforces that exist between the ambient air and the rotating wheel createa peripheral air flow which passes into the shroud and separates thecontact wheel from the periphery of the grinding wheel thereby creatinga restricted'air flow passage. This passage is maintained relativelyconstant in size regardless of changes in the diameter of the wheel, andthe presence of air flowing through the passage prevents actualfrictional engagement of the contact wheel with the periphery of thegrinding wheel thereby preventing wear of the contact wheel. Movement ofthe contact wheel toward the axis of rotation of the grinding wheel dueto wear of the periphery of the grinding wheel results in movement ofthe lever that supports the contact wheel thereby creating anappropriate compensating adjustment of the workpiece supportingplatform.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING FIG. 1 is a sideelevation view, partly in section, showing the adjustabletool-supporting platform of our invention and the platform adjustinglever mechanism;

FIG. 2 is an end view of the structure shown in FIG.

FIG. 3 is a plan view of the structure of FIG. 1; FIG. 4 is a view ofthe actuating lever of FIG. 1 as seen from the plane of section line 4-4of FIG. 1;

FIG. 5 is a subassembly view of the dressing wheel shown in FIG. 1 asseen from a direction that is perpendicular to the axis of rotation ofthe grinding wheel.

PARTICULAR DESCRIPTION OF THE INVENTION In FIG. 1 reference character 10designates a grinding wheel which is adapted to rotate about axis 12.Numeral 14 designates a tool supporting platform. Supporting brackets 16and 18 are carried by the platform 14 at its underside. These straddlebracket 20, which is bolted or otherwise secured to plate 22. Plate 22is mounted in a horizontal position and is supported by side plates 24and 26. These in turn are supported by plate 28, which is bolted orotherwise secured to slide plate 30.

Rollers 32 and 34 engage the underside of one margin of the slide plate30. Another pair of rollers 36 engage the opposite margin of the slideplate 30. Rollers 32 are supported by pins that are carried by the plate38 at an angle of approximately 45. This is best seen in FIG. 2. Theadjacent margin of plate 30 is formed with a flat 40 disposed at anangle that permits rolling engagement thereon of the rollers 33.

Rollers 36 on the opposite side of the slide plate 30 are journalled onsupport wall 42 for rotation about a horizontal axis. Wall 42 alsosupports pins which journal side rollers 44 which engage a flat 46formed on the slide plate 30 at an angle that complements the angle forthe flat 40.

The support walls 38 and 42 are joined to a horizontal base plate 48. Asheet metal shroud 50 is attached to the slide plate 30 and envelops therollers 33. A corresponding sheet metal shroud 52 envelops the rollers44.

As seen in FIG. 1, a connector plate 52 is carried by one end of theslide plate 30. An eyelet 54 is secured to the plate 52 by means of aresilient coupling connection 56. A link 58 is pinned to the eyelet 54as indicated in FIG. 1. The opposite end of the link 58 is connected bymeans of a pin to the lower end 60 of actuating lever 62. The link 58includes a turnbuckle 64 which is adapted to change the effective lengthof the link 58 when his turned.

The plate 52 is connected also to one end of the piston rod 65 whichforms a part of a hydraulic damper 68. The damper comprises, in additionto the rod 65, a cylinder 70 which cooperates with a piston in thecylinder 68 to define a fluid damper chamber. The cylinder 70 isconnected to the stationary base plate 48. Damper 68 resists suddenmovement of the slide plate 30 in one direction or the other, therebypreventing sudden movements of platform 14 due to shock loading or dueto inadvertent manipulation by the operator.

Lever 62 is supported on rocker shaft 66. Shaft 66 in turn is endsupported by spaced bearings 69 and 71 carried by hearing supports whichare adapted to be secured to a stationary portion of the mechanism. Theend 72 of the lever 62 carries a contact wheel support 74. This supportcomprises two arms which carry mounting pin 76. Contact wheel 78 isjournalled on pin 76 and is adapted to engage the periphery 80 of thegrinding wheel 10. A sheet metal shroud 82 is carried by the support 74and it includes two side portions, one portion extending directlyadjacent each side of the grinding wheel 10. The sides of the shroud 82and the periphery of the grinding wheel define an air pocket 84 whichreceives air that is set into peripheral motion due to the rotation ofthe grinding wheel 10. This develops a slight increase in the staticpressure in the air pocket 84 relative to the ambient air pressure whichin turn tends to create a force on the end 72 of lever 62 causing theperiphery of the wheel 78 to separate from the periphery of the grindingwheel 10. This introduces a small air flow passage through which the airin pocket 84 may pass. As the periphery of the wheel 78 becomesseparated from the grinding wheel, lever 62 pivots slightly in aclockwise direction, as viewed in FIG. 1. This motion is translated intoaxial motion of the slide plate 30. This motion then causes thecorresponding adjustment of the platform 14.

The angular position of the platform 14 relative to a horizontalreference line is controlled by adjusting nuts 86 and 88 and adjustingbolt 90. The angular position of the platform 14 can be adjusted byloosening nuts 86 and 88 and then retightening them so that the members16 and 18 frictionally engage the member 20.

When the grinding wheel is at rest with the contact wheel 78 engagingits periphery, the platform 14 may be adjusted by appropriatelypositioning the turnbuckle 64. When the grinding wheel begins to rotate,peripheral air circulation occurs due to the viscous drag of the wheelon the ambient air thereby creating a static pressure increase inchamber 84 which causes lever 62 to move slightly in a clockwisedirection. This backs off the platform 14. A counterweight 91, which iscarried at one end of the counterweight lever 92, causes acounterbalance torque to act upon the lever 62. The end of the lever 62is secured to the clamping structure 94 that forms a connection betweenthe rocker shaft 66 and the lever 62. The amount of oscillatory movementof the lever 62 is decreased as the counterweight 91 moves outwardlyfrom the axis of the shaft 66. Locking bolt 96 holds the counterweight90 in its adjusted position on the shaft 92.

A dressing wheel 98 is carried by a pin 100 which is end supported bysupporting brackets 102 and 104. These brackets are carried by slideplate 105 which is adapted to slide transversely on the plate 22.Guideways 108 and 110 may be provided in the plate 22 to receive guiderails carried by the plate 106. The end of plate 106 carries an endplate 112 through which screw 114 is received. An internally threadedmember 116 receives the screw 114 and is carried by the plate 106, thelatter being mounted over an opening in plate 22 through which themember 116 extends. The end of the screw 116 carries adjusting crankhandle 118. As the handle 118 is rotated in one direction or the otherthe dressing wheel 98 is moved across the periphery of the grindingwheel 10.

As the diameter of the grinding wheel 10 decreases, the lever 62 will beadjusted in a counterclockwise direction. This adjustment then isaccomplished by a corresponding adjustment of the platform 14 toward thegrinding wheel. Thus the clearance between the platform 14 and thegrinding wheel is maintained constant regardless of changes in diameterof the grinding wheel.

The damper 68 normally will not provide appreciable resistance to slowadjusting movements of the lever 62. It will, however, providesubstantial damping forces if the lever 62 for some reason should bemoved abruptly. This prevents damage to the platform 14 and the grindingwheel 10 as well as to the tool being ground.

What we claim and desire to secure by U. S. Letters Patent is:

l. A workholder for a grinding wheel comprising a platform mounted forreciprocating movement toward and away from the axis of rotation of agrinding wheel with one part of the platform in close proximity to theperiphery of the grinding wheel, an adjusting lever mounted foroscillation on a stationary axis, one end of said lever being connectedmechanically to said platform, a contact member carried by said leverand engageable with the periphery of said wheel when the wheel is atrest, said contact member and the periphery of said wheel defining inpart an air flow passage that receives air set in motion due to theshear forces that exist between the ambient air and the rotating wheel,the force established by the resulting air pressure on said levercausing compensating adjustments of said platform upon changes in thediameter wheel due to wear said contact member comprising a contactroller wheel carried by one end of said lever, the periphery of saidroller wheel engaging the periphery of said grinding wheel when thegrinding wheel is stationary and moving away from the periphery of saidgrinding wheel due to static pressure forces created by air circulationupon rotation of said grinding wheel.

2. A workholder for a grinding wheel comprising a platform mounted forreciprocating movement toward and away from the axis of rotation of agrinding wheel with one part of the platform in close proximity to theperiphery of the grinding wheel, an adjusting lever mounted foroscillation on a stationary axis, one end of said lever being connectedmechanically to said platform, a contact member carried by said leverand engageable with the periphery of said wheel when the wheel is atrest, said contact member and the periphery of said wheel defining inpart an air flow passage that receives air set in motion due to theshear forces that exist between the ambient air and the rotating wheel,the force established by the resulting air pressure on said levercausing compensating adjustments of said platform upon changes in thediameter wheel due to wear, said platform includes a horizontal memberdefining a horizontal work supporting surface, a stationary base,friction reducing mounting means for establishing relativelyfriction-free translatory movement of said platform along said base in adirection perpendicular to the axis of rotation of said grinding wheel,and means for normally urging said lever in one angular directionthereby tending to cause said contact member to engage the periphery ofsaid wheel said contact member comprising a contact roller wheel carriedby one end of said lever, the periphery of said roller wheel engagingthe periphery of said grinding wheel when the grinding wheel isstationary and moving away from the periphery of said grinding wheel dueto static pressure forces created by air circulation caused by rotationof said grinding wheel.

3. A workholder for a grinding wheel comprising a platform mounted forreciprocating movement toward aand away from the axis of rotation of agrinding wheel with one part of the platform in close proximity to theperiphery of the grinding wheel, an adjusting lever mounted foroscillation on a stationary axis, one end of said lever being connectedmechanically to said platform, a contact member carried by said leverand engageable with the periphery of said wheel when the wheel is atrest, said contact member and the periphery of said wheel defining inpart an air flow passage that receives air set in motion due to theshear forces that exist between the ambient air and the rotating wheel,the force established by the resulting air pressure on said levercausing compensating adjustments of said platform upon changes in thediameter wheel due to wear, said contact member comprising a contactroller wheel carried by one end of said lever, the periphery of saidroller wheel engaging the periphery of said grinding wheel when thegrinding wheel is stationary and moving away from the periphery of saidgrinding wheel due to static pressure forces created by air circulationupon rotation of said grinding wheel, the connection between said leverand said platform comprising relatively rotatable threaded parts wherebythe effective length of said connection may be varied as desired therebyproviding a predetermined initial position of said platform relative tothe periphery of said wheel.

4. A workholder for a grinding wheel comprising a platform mounted forreciprocating movement toward and away from the axis of rotation of agrinding wheel with one part of the platform in close proximity to theperiphery of the grinding wheel, an adjusting lever mounted foroscillation on a stationary axis, one end of said lever being connectedmechanically to said platform, a contact member carried by said leverand engageable with the periphery of said wheel when the wheel is atrest, said contact member and the periphery of said wheel defining inpart an air flow passage that receives air set in motion due to theshear forces that exist between the ambient air and the rotating wheel,the force established by the resulting air pressure on said levercausing compensating adjustments of said platform upon changes in thediameter wheel due to wear, said platform includes a horizontal memberdefining a horizontal work supporting surface, a stationary base,friction reducing mounting means for establishing relativelyfriction-free translatory movement of said platform along said base in adirection perpendicular to the axis of rotation of said grinding wheel,and means for normally urging said lever in one angular directionthereby tending to cause said contact member to engage the periphery ofsaid wheel, said contact member comprising a contact roller wheelcarried by one end of said lever, the periphery of said roller wheelengaging the periphery of said grinding wheel when the grinding wheel isstationary and moving away from the periphery of said grinding wheel dueto static pressure forces created by air circulation caused by rotationof said grinding wheel, the connection between said lever and saidplatform comprising relatively rotatable threaded parts whereby theeffective length of said connection may be varied as desired therebyproviding a predetermined initial position of said platform relative tothe periphery of said wheel.

5. A workholder for a grinding wheel comprising a platform mounted forreciprocating movement toward and away from the axis of rotation of agrinding wheel with one part of the platform in close proximity to theperiphery of the grinding wheel, an adjusting lever mounted foroscillation on a stationary axis, one end of said lever being connectedmechanically to said platform, a contact member carried by said leverand engageable with the periphery of said wheel when the wheel is atrest, said contact member and the periphery of said wheel defining inpart an air flow passage that receives air set in motion due to theshear forces that exist between the ambient air and the rotating wheel,the force established by the resulting air pressure on said levercuasing compensating adjustments of said platform upon changes in thediameter wheel due to wear, said contact member comprising a contactroller wheel carried by one end of said lever, the periphery of saidroller wheel engaging the periphery of said grinding wheel when thegrinding wheel is stationary and moving away from the periphery of saidgrinding wheel due to static pressure forces created by air circulationupon rotation of said grinding wheel, said platform comprising a fluiddamper having relatively movable parts, one part being connected to astationary portion of said workholder and the other part being connectedto movable portions of said platform whereby dampening forces resistdisplacement of said platform due to excessive loads.-

6. A workholder for a grinding wheel comprising a platform mounted forreciprocating movement toward and away from the axis of rotation of agrinding wheel with one part of the platform in close proximity to theperiphery of the grinding wheel, an adjusting lever mounted foroscillation on a stationary axis, one end of said lever being connectedmechanically to said platform, a contact member carried by said leverand engageable with the periphery of said wheel when the wheel is atrest, said contact member and the periphery of said wheel defining inpart an air flow passage that receives air set in motion due to theshear forces that exist between the ambient air and the rotating wheel,the force established by the resulting air pressure on said levercausing compensating adjustments of said platform upon changes in thediameter wheel due to wear, said platform includes a horizontal memberdefining a horizontal work supporting surface, a stationary base,friction reducing mounting means for establishing relativelyfriction-free translatory movement of said platform along said base in adirection perpendicular to the axis of rotation of said grinding wheel,and means for normally urging said lever in one angular directionthereby tending to cause said contact member to engage the periphery ofsaid wheel, said contact member comprising a contact roller wheelcarried by one end of said lever, the periphery of said roller wheelengaging the periphery of said grinding wheel when the connected to astationary portion of said workholder and the other part being connectedto movable portions of said platform whereby dampening forces resistdisplacement of said platform clue to excessive loads.

1. A workholder for a grinding wheel comprising a platform mounted forreciprocating movement toward and away from the axis of rotation of agrinding wheel with one part of the platform in close proximity to theperiphery of the grinding wheel, an adjusting lever mounted foroscillation on a stationary axis, one end of said lever being connectedmechanically to said platform, a contact member carried by said leverand engageable with the periphery of said wheel when the wheel is atrest, said contact member and the periphery of said wheel defining inpart an air flow passage that receives air set in motion due to theshear forces that exist between the ambient air and the rotating wheel,the force established by the resulting air pressure on said levercausing compensating adjustments of said platform upon changes in thediameter wheel due to wear said contact member comprising a contactroller wheel carried by one end of said lever, the periphery of saidroller wheel engaging the periphery of said grinding wheel when thegrinding wheel is stationary and moving away from the periphery of saidgrinding wheel due to static pressure forces created by air circulationupon rotation of said grinding wheel.
 2. A workholder for a grindingwheel comprising a platform mounted for reciprocating movement towardand away from the axis of rotation of a grinding wheel with one part ofthe platform in close proximity to the periphery of the grinding wheel,an adjusting lever mounted for oscillation on a stationary axis, one endof said lever being connected mechanically to said platform, a contactmember carried by said lever and engageable with the periphery of saidwheel when the wheel is at rest, said contact member and the peripheryof said wheel defining in part an air flow passage that receives air setin motion due to the shear forces that exist between the ambient air andthe rotating wheel, the force established by the resulting air pressureon said lever causing compensating adjustments of said platform uponchanges in the diameter wheel due to wear, said platform includes ahorizontal member defining a horizontal work supporting surface, astationary base, friction reducing mounting means for establishingrelatively friction-free translatory movement of said platform alongsaid base in a direction perpendicular to the axis of rotation of saidgrinding wheel, and means for normally urging said lever in one angulardirection thereby tending to cause said contact member to engage theperiphery of said wheel said contact member comprising a contact rollerwheel carried by one end of said lever, the periphery of said rollerwheel engaging the periphery of said grinding wheel when the grindingwheel is stationary and moving away from the periphery of said grindingwheel due to static pressure forces created by air circulation caused byrotation of said grinding wheel.
 3. A workholder for a grinding wheelcomprising a platform mounted for reciprocating movement toward and awayfrom the axis of rotation of a grinding wheel with one part of theplatform in close proximity to the periphery of the grinding wheel, anadjusting lever mounted for oscillation on a stationary axis, one end ofsaid lever being connected mechanically to said platform, a contactmember carried by said lever and engageable with the periphery of saidwheel when the wheel is at rest, said contact member and the peripheryof said wheel defining in part an air flow passage that receives air setin motion due to the shear forces that exist between the ambient air andthe rotating wheel, the force established by the resulting air pressureon said lever causing compensating adjustments of said platform uponchanges in the diameter wheel due to wear, said contact membercomprising a contact roller wheel carried by one end of said lever, theperiphery of said roller wheel engaging the periphery Of said grindingwheel when the grinding wheel is stationary and moving away from theperiphery of said grinding wheel due to static pressure forces createdby air circulation upon rotation of said grinding wheel, the connectionbetween said lever and said platform comprising relatively rotatablethreaded parts whereby the effective length of said connection may bevaried as desired thereby providing a predetermined initial position ofsaid platform relative to the periphery of said wheel.
 4. A workholderfor a grinding wheel comprising a platform mounted for reciprocatingmovement toward and away from the axis of rotation of a grinding wheelwith one part of the platform in close proximity to the periphery of thegrinding wheel, an adjusting lever mounted for oscillation on astationary axis, one end of said lever being connected mechanically tosaid platform, a contact member carried by said lever and engageablewith the periphery of said wheel when the wheel is at rest, said contactmember and the periphery of said wheel defining in part an air flowpassage that receives air set in motion due to the shear forces thatexist between the ambient air and the rotating wheel, the forceestablished by the resulting air pressure on said lever causingcompensating adjustments of said platform upon changes in the diameterwheel due to wear, said platform includes a horizontal member defining ahorizontal work supporting surface, a stationary base, friction reducingmounting means for establishing relatively friction-free translatorymovement of said platform along said base in a direction perpendicularto the axis of rotation of said grinding wheel, and means for normallyurging said lever in one angular direction thereby tending to cause saidcontact member to engage the periphery of said wheel, said contactmember comprising a contact roller wheel carried by one end of saidlever, the periphery of said roller wheel engaging the periphery of saidgrinding wheel when the grinding wheel is stationary and moving awayfrom the periphery of said grinding wheel due to static pressure forcescreated by air circulation caused by rotation of said grinding wheel,the connection between said lever and said platform comprisingrelatively rotatable threaded parts whereby the effective length of saidconnection may be varied as desired thereby providing a predeterminedinitial position of said platform relative to the periphery of saidwheel.
 5. A workholder for a grinding wheel comprising a platformmounted for reciprocating movement toward and away from the axis ofrotation of a grinding wheel with one part of the platform in closeproximity to the periphery of the grinding wheel, an adjusting levermounted for oscillation on a stationary axis, one end of said leverbeing connected mechanically to said platform, a contact member carriedby said lever and engageable with the periphery of said wheel when thewheel is at rest, said contact member and the periphery of said wheeldefining in part an air flow passage that receives air set in motion dueto the shear forces that exist between the ambient air and the rotatingwheel, the force established by the resulting air pressure on said levercuasing compensating adjustments of said platform upon changes in thediameter wheel due to wear, said contact member comprising a contactroller wheel carried by one end of said lever, the periphery of saidroller wheel engaging the periphery of said grinding wheel when thegrinding wheel is stationary and moving away from the periphery of saidgrinding wheel due to static pressure forces created by air circulationupon rotation of said grinding wheel, said platform comprising a fluiddamper having relatively movable parts, one part being connected to astationary portion of said workholder and the other part being connectedto movable portions of said platform whereby dampening forces resistdisplacement of said platform due to excessive loads.
 6. A workholderfor a grinding wheel comprising a plaTform mounted for reciprocatingmovement toward and away from the axis of rotation of a grinding wheelwith one part of the platform in close proximity to the periphery of thegrinding wheel, an adjusting lever mounted for oscillation on astationary axis, one end of said lever being connected mechanically tosaid platform, a contact member carried by said lever and engageablewith the periphery of said wheel when the wheel is at rest, said contactmember and the periphery of said wheel defining in part an air flowpassage that receives air set in motion due to the shear forces thatexist between the ambient air and the rotating wheel, the forceestablished by the resulting air pressure on said lever causingcompensating adjustments of said platform upon changes in the diameterwheel due to wear, said platform includes a horizontal member defining ahorizontal work supporting surface, a stationary base, friction reducingmounting means for establishing relatively friction-free translatorymovement of said platform along said base in a direction perpendicularto the axis of rotation of said grinding wheel, and means for normallyurging said lever in one angular direction thereby tending to cause saidcontact member to engage the periphery of said wheel, said contactmember comprising a contact roller wheel carried by one end of saidlever, the periphery of said roller wheel engaging the periphery of saidgrinding wheel when the grinding wheel is stationary and moving awayfrom the periphery of said grinding wheel due to static pressure forcescreated by air circulation caused by rotation of said grinding wheel,said platform comprising a fluid damper having relatively movable parts,one part being connected to a stationary portion of said workholder andthe other part being connected to movable portions of said platformwhereby dampening forces resist displacement of said platform due toexcessive loads.